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Bulk earthworks progressed well across the entire route over summer, with the weather and commitment of the entire project team playing key roles

Major milestones for Transmission Gully – By Iain MacIntyre

Significant milestones are being reached at major interchanges within the Transmission Gully project, including beams recently being placed on a future flyover at State Highway 58 and traffic about to be switched onto a new bridge at the southern tie-in point of State Highway 1.

Transmission Gully construction project director Justin Redelinghuys says the SH58 interchange at Lanes Flat is “shaping up nicely” with the beams already in place on the new overbridge (Bridge 13).

“Bridge 13 carries the Transmission Gully main 
alignment over SH58 and is located at approximate chainage 17,280 m,” he says. “It is a single-span structure, 37.39 m in length, that caters for four traffic lanes (two in each direction), shoulders and the central median of the main alignment.

“The superstructure consists of 13 precast pre-stressed Super-T beams, each 1525 mm deep and weighing 64 tonnes, with an in-situ reinforced concrete deck which will be constructed on a 6% cross fall, and is fully integral with the abutments. The overall deck width to the outside face of the barriers is 26 m and the beams have been placed using a 400 tonne crawler crane. Construction has been progressing well and we are on track to complete Bridge 13 in November.”

Beams for Bridge 13 were placed using a 400 tonne crawler crane – construction of the bridge is on track for completion in November 

Realigning SH58

Key components of the phased construction works at the site – which is located near the middle of the 27 km motorway and is where the project team has established its main site office – include a diversion that first had to be built so as to redirect the Pauatahanui Stream, which previously meandered through the site. Being a flood plain, soils then needed strengthening under all structures, with a lattice of hundreds of stone columns at 1 m centres.

The focus then progressively moved onto earthworks for the embankments, construction of mechanically stabilised earth (MSE) and reinforced earth (RE) walls for bridge abutments, the new SH58 road realignment and associated roundabouts to connect to on and off-ramps (with it being noted that the new SH58 road is slightly higher than the old one so as to lift it out of the floodplain).

Mr Redelinghuys says the realignment of SH58 is planned to occur before Christmas this year. “We can’t build the north side of Bridge 13 until this happens as we need to build an embankment across the existing state highway.”

Graphic of the SH58 realignment, overbridges for the Transmission Gully main alignment and associated roundabouts

SH1 southern tie-in

Meanwhile, at the southern tie-in point of the motorway, Mr Redelinghuys says work has advanced to replace the existing four-lane bridge on SH1 – which goes over Collins Avenue in Linden – with a new six-lane bridge (Bridge 26).

“We do this in three stages of building two lanes at a time and switching the SH1 traffic over to free up room for the next stage. At the end of September, we switch SH1 over onto the first part of the new bridge, and over the next few days demolish two lanes of the old bridge over Collins Avenue. We then begin construction of the second section of new bridge in a worksite between the north and southbound lanes of SH1.”

Mr Redelinghuys says the team is very focused on preparation for the upcoming switchover to the new bridge, which is about 2 m higher than the old structure, including via building approach embankments to tie in to the existing lanes.

“As part of this work, in August we will be making the road wider on each side of the motorway south of the Mungavin Interchange to just past Tawa College. This allows for the demolition of the old Collins Avenue overbridge and also provides a larger working area in the central median for building the central columns for Bridge 25 (the northbound ramp onto Transmission Gully) and Bridge 27 (the Kenepuru Link Road over SH1).”

Mr Redelinghuys says the majority of this realignment work will be done at night to minimise disruption from the necessary lane closures. “Once the lanes are realigned, daytime southbound speed limits will also be reduced to 70 kph to ensure driver safety through areas where the concrete barriers may temporarily affect lines of sight. The reduced speeds are also vital for the safety of our teams working alongside the live traffic lanes, so we ask drivers to please pay close attention to the signage and keep to the posted speed limits.”

Halfway point passed

Another key milestone passed at the end of May – which officially marked the end of the summer earthworks season – was the team having progressed beyond the halfway mark for construction of the 27 km motorway.

Mr Redelinghuys says bulk earthworks have “progressed well” across the entire route over summer, with the weather and commitment of the entire project team playing key roles. “With two years of physical works left to go, we’re in a great position moving into the next phases of works for the new motorway.”

Wellington Gateway Partnership (WGP) chief executive Sergio Mejia is also “extremely pleased” with the progress achieved. “We are on schedule to complete what will be one of New Zealand’s safest, most resilient – not to mention most keenly-anticipated motorways – in 2020,” says Mr Mejia.

At its peak this summer, the project had a workforce of over 950 people. Since works began on the project, over 4 million work hours have been completed.

Key overall project milestones achieved as at the end of May include:

• 50% of motorway construction completed

• 6 million cu m of earth moved

• 5 km of gas pipeline relocations completed

• Four of the project’s 27 structures completed

• 8 km of the new motorway at pre-pavement level completed

• 1.5 km of permanent stream diversions created.


Safety through innovation

In addition to having strict environmental controls in place to mitigate the risk of damage in that sphere, the project team is also trialling innovative technology to increase the safety of workers onsite.

The Hunter Safety Lab and project teams are 
field-testing the IRIS (infrared retro-reflector identification system) Detect product, which is designed to enhance safety practices involving people working near mobile plant, explains Hunter Safety Lab founder David Grove.

All workers are removed from machinery-operating zones to eliminate interaction

“IRIS Detect recognises the reflector strips within high-vis vests, meaning that the system conforms to the user, or, in this case, anyone who is wearing a high-vis vest,” he says. “The most significant advantage of this technology over most other industrial pedestrian-detection systems is that it doesn’t require ground staff to carry an electronic tag or change their behaviour in any way.”

Sensors mounted on machinery continuously emit pulses of non-visible light into blind spots around a machine and the driver receives an audio-visual alert if someone is detected in the blind spot.

Mr Redelinghuys is very supportive of the development, particularly given that the Transmission Gully motorway is a “very busy construction site” with over 600 people and over 200 items of machinery at work.

He notes that field trials have included use of an articulated mobile crane, which reverses as part of its normal activities. “As part of our current health and safety practices, all workers are removed from machinery-operating zones to eliminate interaction. However, this technology gives another layer of protection to help the operator ensure the machinery operation zone is clear and safe for movement.”

Adds Mr Mejia: “It’s important that we promote and support this sort of technology. We’re always looking at ways to improve what we do, and if, as an industry, we don’t support development of innovation, we are the poorer for it.”

Landscaping and planting

While the project team began planting some small areas last year, it has recently ramped up its extensive planting programme.

“By the time the motorway opens, we will have established in excess of 2 million plants,” continues Mr Redelinghuys. “Some are for landscaping purposes, but most are planted in ecological areas to mitigate the effects of construction on terrestrial, marine and freshwater habitats. We have started taking delivery of the first batches of the specifically-propagated plants, and will have more information in coming months about how planting is progressing.”

On target

A public private partnership (PPP) launched between the New Zealand Transport Agency (NZTA) and the WGP in late 2014, the $850 million Transmission Gully project currently remains on budget and on schedule for completion in 2020.

Iain MacIntyre is an award-winning journalist who specialises in transport and infrastructure issues within New Zealand i.macintyre@xtra.co.nz

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